linux-kernel - Re: [PATCH 0/4] Fix Samsung pinctrl driver static allocation of GPIO base warning

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Message-ID: <CAPLW+4nyLunQw+wCxQmw9VDCGx2ECeAhUzjKRCBeHW7fGS1dFA@mail.gmail.com>
Date:   Sun, 8 Oct 2023 13:45:42 -0500
From:   Sam Protsenko <semen.protsenko@...aro.org>
To:     Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>
Cc:     Mateusz Majewski <m.majewski2@...sung.com>,
        linux-arm-kernel@...ts.infradead.org,
        linux-samsung-soc@...r.kernel.org, linux-gpio@...r.kernel.org,
        linux-kernel@...r.kernel.org, Tomasz Figa <tomasz.figa@...il.com>,
        Sylwester Nawrocki <s.nawrocki@...sung.com>,
        Alim Akhtar <alim.akhtar@...sung.com>,
        Linus Walleij <linus.walleij@...aro.org>,
        Marek Szyprowski <m.szyprowski@...sung.com>
Subject: Re: [PATCH 0/4] Fix Samsung pinctrl driver static allocation of GPIO
 base warning

On Sun, Oct 8, 2023 at 8:09 AM Krzysztof Kozlowski
<krzysztof.kozlowski@...aro.org> wrote:
>
> On 07/10/2023 04:14, Sam Protsenko wrote:
> > On Fri, Oct 6, 2023 at 8:01 AM Mateusz Majewski <m.majewski2@...sung.com> wrote:
> >>
> >> The object of this work is fixing the following warning, which appears
> >> on all targets using that driver:
> >>
> >> gpio gpiochip0: Static allocation of GPIO base is deprecated, use dynamic allocation.
> >>
> >> This needs a small refactor to how we interact with the pinctrl
> >> subsystem. Finally, we remove some bookkeeping that has only been
> >> necessary to allocate GPIO bases correctly.
> >>
> >> Mateusz Majewski (4):
> >>   pinctrl: samsung: defer pinctrl_enable
> >>   pinctrl: samsung: use add_pin_ranges method to add pinctrl ranges
> >>   pinctrl: samsung: choose GPIO numberspace base dynamically
> >>   pinctrl: samsung: do not offset pinctrl numberspaces
> >>
> >>  drivers/pinctrl/samsung/pinctrl-samsung.c | 56 ++++++++++++-----------
> >>  drivers/pinctrl/samsung/pinctrl-samsung.h |  4 +-
> >>  2 files changed, 31 insertions(+), 29 deletions(-)
> >>
> >> --
> >
> > Hi Mateusz,
> >
> > Thank you for handling this! Those deprecation warnings have been
> > bugging me for some time :) While testing this series on my E850-96
> > board (Exynos850 based), I noticed some changes in
> > /sys/kernel/debug/gpio file, like these:
> >
> > 8<------------------------------------------------------------------------------------------>8
> > -gpiochip0: GPIOs 0-7, parent: platform/11850000.pinctrl, gpa0:
> > - gpio-7   (                    |Volume Up           ) in  hi IRQ ACTIVE LOW
> > +gpiochip0: GPIOs 512-519, parent: platform/11850000.pinctrl, gpa0:
> > + gpio-519 (                    |Volume Up           ) in  hi IRQ ACTIVE LOW
> >
> > -gpiochip1: GPIOs 8-15, parent: platform/11850000.pinctrl, gpa1:
> > - gpio-8   (                    |Volume Down         ) in  hi IRQ ACTIVE LOW
> > +gpiochip1: GPIOs 520-527, parent: platform/11850000.pinctrl, gpa1:
> > + gpio-520 (                    |Volume Down         ) in  hi IRQ ACTIVE LOW
> >
> > -gpiochip2: GPIOs 16-23, parent: platform/11850000.pinctrl, gpa2:
> > +gpiochip2: GPIOs 528-535, parent: platform/11850000.pinctrl, gpa2:
> >
> > ...
> > 8<------------------------------------------------------------------------------------------>8
> >
> > So basically it looks like all line numbers were offset by 512. Can
> > you please comment on this? Is it an intentional change, and why it's
> > happening?
> >
> > Despite of that change, everything seems to be working fine. But I
> > kinda liked the numeration starting from 0 better :)
>
> Could it be the reason of dynamic allocation?
>

I just asked because I didn't know :) But ok, if you want me to do
some digging... It seems like having GPIO_DYNAMIC_BASE=512 is not
necessarily the reason of dynamic allocation, but instead just a way
to keep 0-512 range for legacy GPIO drivers which might use that area
to allocate GPIO numbers statically. It's mentioned here:

    /*
     * At the end we want all GPIOs to be dynamically allocated from 0.
     * However, some legacy drivers still perform fixed allocation.
     * Until they are all fixed, leave 0-512 space for them.
     */
    #define GPIO_DYNAMIC_BASE    512

As mentioned in another comment in gpiochip_add_data_with_key(), that
numberspace shouldn't matter and in the end should go away, as GPIO
sysfs interface is pretty much deprecated at this point, and everybody
should stick to GPIO descriptors.

Anyway, now that it's clear that the base number change was intended
and shouldn't matter, for all patches in the series:

Reviewed-by: Sam Protsenko <semen.protsenko@...aro.org>
Tested-by: Sam Protsenko <semen.protsenko@...aro.org>

Thanks!

>
> Best regards,
> Krzysztof
>